The present invention relates to an aluminium alloy having high strength and low quench sensitivity. Also within the scope of the invention is a process for manufacturing thick plates of the aluminium alloy.
In particular in the automobile industry there is an increasing demand for large plastic components such as e.g. integral bumpers. In order to manufacture the corresponding large moulds for injection moulding purposes it is necessary to have plates with a thickness often greater than 150 mm, in some cases even greater than 500 mm.
Today, normally hot rolled and artificially aged, i.e. plates heat-treated at elevated temperature, are employed for manufacturing injection moulding moulds with a thickness e.g. of 50 to 300 mm. Larger moulds, thicker than 300 mm, are manufactured either out of forged blocks or directly from continuously cast ingots.
One significant disadvantage of the aluminium alloys employed today for mould manufacture is their high quench sensitivity. In order that the ingots or plates reach the necessary strength level for plastic injection moulding moulds by means of artificial age hardening, the rate of cooling from the homogenisation or solution treatment temperature has to be increased with increasing plate thickness. Due to the resultant high temperature gradients between the surface and the core of the ingot or plate, the magnitude of the undesirable internal stresses increases, so that also for this reason there are limits to increasing the cooling rate further and with that the strength level that can be reached.
An object of the invention is to provide a suitable aluminium alloy of low quench sensitivity for manufacturing thick plates having a high strength level.
A further objective of the invention is to provide a suitable process by means of which the aluminium alloy can be processed to thick plates having adequate high strength over the whole plate thickness.